The present invention relates to a method and apparatus for measuring the volume or weight of a fluid, such as measuring the volume of blood or urine in a transfusion or autotransfusion system employed in a cardiac intensive care unit (CICU). More particularly, the invention relates to the measurement of the volume of a fluid in a container, such as a cardiotomy or urine resvoir, employing a load cell transducer.
During the immediate recovery of post-operative cardiovascular surgery patients, CICU nurses are responsible for carrying out several tasks. These include the management of the patient's heart rate and rhythm, ventilation, blood pressure, renal function, temperature, and monitoring of chest tube and urine drainage. In the case of serious post operative bleeding, close monitoring of chest tube drainage is critical and replacement of lost blood volume is required. Autotransfusion involves the reinfusion of a patient's own blood as opposed to the transfusion of bank blood. Although intraoperative and postoperative blood conservation techniques have decreased the use of bank blood for cardiac surgical patients, the increasing number of surgical procedures has placed a strain on the bank blood supply. One procedure to reduce this strain is postoperative autotransfusion, the return of blood shed from the mediastinum or thoracic cavity following surgery. The efficacy and safety of postoperative autotransfusion has been documented (Johnson et al., Ann. Thorac. Surg. 1983; 36:178). Furthermore, autotransfusion is the safest form of transfusion therapy because there is no risk of alloimmunization, hepatitis, acquired immunodeficiency syndrome (AIDS), or other complications possible with bank blood. The operation and efficacy of an autotransfusion system is described in U.S. patent application Ser. No. 07/431,296, which is hereby incorporated by reference in its entirety in order to more fully describe the state of the art to which this invention pertains.
Existing autotransfusion systems usually include a cardiotomy reservoir for the collection of blood shed from the patient. The reservoir, which may collect body fluids other than blood, is associated with a lead cell transducer which measures the volume of fluid in the reservoir. A disadvantage of current systems is that the connection between the body fluid container and the lead cell transducer is passive and is susceptible to being bumped or pulled out of alignment. A further disadvantage of existing systems is that there is no automated means for detecting the presence of the reservoir on the lead cell mounting adapter or the proper alignment of the reservoir on the mounting adapter.
A still further disadvantage of existing systems is that there is no automated means for protecting the lead cell transducer from damage resulting from overweighing due to bumping or excess force during the seating of the container on the mounting adapter for the lead cell transducer.
Therefore, there exists a need for a fluid collection system in which the container and lead cell adapter are firmly attached during operation. Further, there exists a need for means, particularly automated means, for detecting the placement and alignment of a container capable of holding a fluid on a lead cell transducer. There also exists a need for protecting the lead cell transducer from damage due to improper movement or positioning of the fluid container.
Throughout this application, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.